The present invention relates to a captive fastener to be attached to a sheet material. More specifically it relates to a captive nut which is particularly suitable for use when a water tight mounting point is required such as on the roof panel of a vehicle, to take a roof rack, or in the vehicle floor pan.
GB-A-1 474 766 describes a nut which is attached to a sheet metal component by a pressing operation. The nut has a tubular end which is pressed into an aperture in the sheet metal, deforming the rim of the aperture into a cylinder to embrace the periphery of the nut. The tubular end is turned around the rim to secure the nut against removal, while a flange at the other end of the nut prevents the nut being pushed completely through the aperture. Such nuts are sold by the present applicants under the trade mark FLANGEFORM. An alternative method of attaching nuts to sheet material is to weld a standard nut to the sheet material. However, welding is less suited to an automated sheet material assembly process which is based around a press, produces unfavourable fumes and also has the undesirable side effect of weld heat damage to the sheet material.
FIGS. 1 and 2 show prior art captive nuts which are used on a press similar to that described in GB-A-1 474 766. When these nuts are pressed into an aperture in a sheet material, the sheet material around the aperture is deformed and the splines which extend from the periphery of the nut indent the sheet material to resist rotation of the nut. FIGS. 3 and 4 show a high torque version of the captive nut and the difference between this nut and the nut of FIGS. 1 and 2 is that the splines are larger than the splines of the captive nut of FIGS. 1 and 2, providing more resistance to rotation of the nut in the aperture. As the splines indent the sheet material, the seam between the nut and the sheet material is not watertight, making these nuts inappropriate for use as attachment points where water proofing is required.
The nuts 1 are comprised of a tubular portion 3 with a flange 5 extending radially from one end 7 of the tubular portion 3. There are six splines 9 equally spaced around the tubular portion 3, the splines extending radially from the tubular portion 3 to the flange 5.
FIG. 5 is a section view through a press 11 in which the nut 1 of FIG. 1 has been attached to a metal sheet material 13. The sheet material 13 around the aperture 15 through which the nut 1 is pressed is deformed to form a collar 17 and the ends 19 of the tubular portion 3 of the nut 1 are deformed to pinch the end 21 of the collar 17. The splines 9 indent the collar 17, thereby resisting rotation of the nut 1 when a rotational force is applied to the nut 1, for example when screwing a bolt into the nut 1.
The splines 9 of the nut 1 of FIGS. 3 and 4 are larger than the splines 9 of the nut 1 of FIGS. 1 and 2, thereby providing greater rotational resistance than the nut 1 of FIGS. 1 and 2, hence the nut 1 of FIGS. 3 and 4 is used in high torque applications. The inside 37 of the nut 1 is threaded so that a bolt or the like can be attached thereto.
When the splines 9 of the nut 1 of FIGS. 1 to 4 indent the collar 17 the seam 23 between the nut 1 and the collar 17 is not watertight. In order to make the seam 23 watertight it has been found necessary to reduce the size of the splines 9, thereby indenting the collar 17 less than the splines 9 of the nut 1 of FIGS. 1 to 4. However, care is required when reducing the size of the splines 9 so that the splines 9 will still provide sufficient resistance to a rotational force.
A roof rack can be used on a vehicle to increase the carrying capacity of the vehicle. Various methods exist to fix a roof rack to a vehicle. Attachment points are commonly provided to facilitate attachment of a roof rack. The attachment points may typically be a flange or recess running along either longitudinal side of the roof. Often these flanges are masked by a rubber strip or by a plastic strip with flaps which slide back to reveal the flange. In general these attachments points or covering strips can be unsightly and car designers often attempt to disguise these attachment points.
It is one aim of the invention to provide an improved fixing point for a vehicle roof rack.
It is another aim of the present invention to provide a captive nut which forms a watertight seal with a sheet material while resisting rotation when a bolt or other device is screwed into it.